\documentclass{standalone}
\usepackage{tikz}

\usepackage{../../style/csmacros}

\usepackage{color}
\definecolor{blueedf}{RGB}{0,91,187}
\definecolor{orangededf}{RGB}{254,88,21}

\newcommand{\orange}[1]{
\textcolor{orangededf}{#1}}
\newcommand{\blue}[1]{
\textcolor{blueedf}{#1}}

\begin{document}
\begin{tikzpicture}[scale=0.3, transform shape]
      % Fluid Region
      %   Cell i
      \draw (3,4)  -- (6,6) -- (10,4) -- (12,0) -- (9,-3) -- (5,-1) [white,fill=blue!10];
      %   Cell j
      \draw (10,4) -- (14,8) -- (21,6) -- (21,2) -- (17,0) -- (12,0) [white,fill=blue!10];
      % Mesh
      % Cell i
      \draw[orange] (3,4)  -- (6,6) -- (10,4) -- (12,0) -- (9,-3) -- (5,-1) -- cycle ;
      \draw[orange] (5,1.5) node[above]{\Huge $\orange{\Omega_{\celli}}$};
      % Cell j
      \draw[orange] (10,4) -- (14,8) -- (21,6) -- (21,2) -- (17,0) -- (12,0) -- cycle ;
      \draw[orange] (16,6) node[above]{\Huge $\orange{\Omega_{\cellj}}$};
      %contour cells
      \draw[orange] (3,4)  -- (2,4) ;
      \draw[orange] (5,-1) -- (2,-5) ;
      \draw[orange] (6,6)  -- (5,8) ;
      \draw[orange] (9,-3) -- (10,-5) ;
      \draw[orange] (10,4) -- (12,6) ;
      \draw[orange] (12,0)  -- (14,0) ;
      \draw[blueedf,line width=1.] (10,4) -- (12,0);
      %   Line IJ
      \draw (7.8,2) node[black,left]{\Huge $\centi$} ;
      \node[circle,draw=black, fill=black, inner sep=0pt,minimum size=7pt, line width=0.5] (b) at (8,2) {};
      \draw [-,black](8,2) -- (16,3.5);
      \draw (16.2,3.5) node[black,right]{\Huge $\centj$} ;
      \node[circle,draw=black, fill=black, inner sep=0pt,minimum size=7pt, line width=0.5] (b) at (16,3.5) {};
      %   Line I'J'
      \draw [-,dashed,black](8.5,1) -- (15.65,4.2);
      \draw [-,dashed,black](8.5,1) -- (8,2) ;
      \draw [-,dashed,black](15.65,4.2) -- (16,3.5) ;
      \draw (8.5,1) node[black,below]{\Huge $\centip$} ;
      \draw (15.65,4.2) node[black,above]{\Huge $\centjp$} ;
      % Angles
      \draw (8.5,1) -- (8.7,1.1) -- (8.6,1.3) -- (8.4,1.2) -- cycle;
      \draw (15.65,4.2) -- (15.75,4) -- (15.55,3.9) -- (15.45,4.1) -- cycle;
      \draw (10.97,2.05) -- (11.17,2.15) -- (11.07,2.35) -- (10.87,2.25) -- cycle;
      %   Points at the face
      \draw [-stealth,blueedf,line width=1.](10.9,2.05) -- (13.5,3.2);
      \draw (13.5,2.7) node[blueedf,below]{\Huge $\vect{S}_{\bij}$};
      \draw (11.1,1.2) node[black,left]{\Huge $\centf$};
      \node[circle,draw=black, fill=black, inner sep=0pt,minimum size=7pt, line width=0.5] (b) at (10.97,2.05) {};
      \node[circle,draw=black, fill=black, inner sep=0pt,minimum size=7pt, line width=0.5] (b) at (10.75,2.5) {};
      \draw (10.75,2.7) node[black,above right]{\Huge $\cento$};

\end{tikzpicture}
\end{document}
